Low-cost power-reducing device for hid lamp

ABSTRACT

Add-on device for high-intensity-discharge lamp and ballast which reduces the wattage at which the lamp is operated. The addon device has two parallel circuit paths, one of which is an RC circuit and the other of which comprises a triac. A diac connects the gate of the triac to the midpoint of the RC circuit to control the time in each half-cycle of energizing potential that the triac fires. The predetermined relative values of the RC components and the rating of the diac control the time of firing of the triac in each half-cycle, and thus determine the wattage at which the lamp is operated.

United States Patent Elms et al. Dec. 9, 1975 [54] LOW-COST POWER-REDUCING DEVICE 3,649,869 3/1972 Nomura et al 315/205 FOR HID LAMP [75] Inventors: Robert T. Ehns, Monroeville, Pa.; jgzfgfgjx gj li y ggt f Merle Keck Bay Vlnage Ohm Attorney, Agent, or Firm-W. D. Palmer [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa. [57] ABSTRACT [22] Filed: May 15, 1974 Add-on device for high-intensity-discharge lamp and t ballast which reduces the wattage at which the lamp is [21] Appl' 470102 operated. The add-on device has two parallel circuit paths, one of which is an RC circuit and the other of [52] US. Cl. 315/246; 315/DIG. 5; 315/205; which comprises a triac. A diac connects the gate of 315/258 the triac to the midpoint of the RC circuit to control [51] Int. Cl. H05B 41/16 the time in each half-cycle of energizing potential that [58] Field of Search 3l5/DIG. 5, 200, 205, 246, the triac fires. The predetermined relative values of 315/258, 272 the RC components and the rating of the diac control the time of firing of the triac in each half-cycle, and [56] References Cited thus determine the wattage at which the lamp is oper- UNITED STATES PATENTS Peek 315/272 X ated.

7 Claims, 3 Drawing Figures us. Patent Dc.9,1975- 3,925,705

CURRENT LIMITING) INDUCTOR CONVENTIONAL LAG TYPE BALLAST FIG.2

BACKGROUND OF THE INVENTION This invention relates to ballasting circuits for discharge lamps and, more particularly, to an add-on device for a discharge lamp and ballast which reduces the wattage at which the lamp operates.

High-intensity-discharge lamps are used for highway and outdoor lighting and also for indoor applications and these are generally known in the art as HID lamps, specific examples being high-pressure mercury-vapor discharge lamps, high-pressure mercury-metal halide lamps and high-pressure sodium-mercury lamps. Such lamps require some sort of ballasting or current limiting device to prevent the discharge from running away and the simplest ballasting technique is to incorporate a current limiting inductor in series with the lamp, with the series-connected lamp and inductor connected across the line. This is known in the art as a lag-type ballast. Such a ballast .may also use a transformer to match line voltage to lamp operating voltage and will also normally incorporate a capacitor connected across the line, in order to correct the power factor.

With the advent of the energy crisis it is desired to eliminate unnecessary lighting and to reduce the necessary lighting wherever possible. In the case of incandescent lamps, lower wattage lamps can be used to reduce the lighting power, but in the case of a high-intensitydischarge lamp, no such simple change can be made, particularly when a lag-type ballast is used. Accordingly, it is highly desirable that some sort of very simple add-on device be available in order to reduce the wattage consumption of high-intensity-discharge lamps so that existing installations can be readily and cheaply altered to operate with a lower wattage input.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided an add-on control device for use with an HID lamp and current-limiting-inductor connected in series therewith, wherein the add-on control device reduces by a predetermined amount the average nominal or rated current passed by the inductor to reduce by a predetermined amount the wattage at which the lamp operates. The add-on control device comprises two electrical circuit paths connected in parallel, with each circuit path connected to terminals which are in turn adapted to be connected in series with the lamp and inductor. One of the circuit paths comprises a series-connected resistor and capacitor each having predetermined electrical values. The other of these circuit paths has therein a solid-state AC control-signal-responsive switching means which has a control terminal. This switching means is responsive to the application of a control signal in order to close during each half cycle of lamp energizing potential and to remain closed the remainder of each such half cycle to supply electrical energy to the lamp in a reduced quantity. There is also provided a solid-state AC voltage-responsive switch means which conducts only when the AC voltage applied thereacross exceeds a predetermined value and this switch means is connected between the control terminal of the AC control-signal-responsive switching means and the midpoint of the RC circuit. When the voltage applied during each half cycle of the energizing potential reaches such value that the voltage-respon- 2 sive switch means conducts, the resulting voltage signal closes the AC control-signal-responsive switching means in order to provide energizing power at a reduced quantity to the lamp.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be had to the preferred embodiment, exemplary of the invention, shown in the accompanying drawings in which:

FIG. 1 is a diagrammatic view of a conventional lagtype ballast for an HID lamp;

FIG. 2 is a diagrammatic view of the conventional ballast as shown in FIG. 1, but with the add-on circuit of the present invention operatively connected in series therewith;

FIG. 3 is a diagrammatic view of an alternative lamp energizing circuit with the add-on circuit, which is shown in block diagram, operatively connected therewith.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the conventional circuit as shown in FIG. I, the lamp 10 by way of example is a high-pressure mercury vapor lamp rated at 400 watts, such as is conventionally used in street lighting. The current limiting inductor 12 which is connected in series therewith has an inductive reactance of 50 ohms and the inductor 12 and lamp 10 are adpated to be connected across the line voltage which typically is 60 Hz, 240 volts. A power-factor correction capacitor 14, which typically has a capacitance of 30p.f, may also be incorporated in the circuit, if desired. The lag-type ballast as shown in FIG. 1 will operate the lamp 10 at about its rated wattage.

The add-on control device of the present invention is shown in FIG. 2. The add-on device 16, which preferably is fabricated as a packaged unit, comprises two electrical circuit paths connected in parallel and each connect to terminals 18, 20 which are adpated to be connected in series with the series-connected lamp 10 and inductor 12. One of the circuit paths comprises a series-connected resistor means 22 and a capacitor means 24, each having predetermined electrical values. As a specific example, for operating the 400 watt lamp at the predetermined reduced wattage, the resistor 22 has a resistance of 39,000 ohms and the capacitor 24 has a capacitance of 0.22 microfarad.

The other of the circuit paths has therein a solid-state AC control-signal-responsive switching means 26 which is responsive to the application of a control signal to the control tenninal28 thereof to close during each half cycle of lamp energizing potential and to remain closed for the remainder of each such half cycle to supply electrical energy to the lamp. As will be clear, the point in time during each half cycle of lamp energizing potential at which the switching means 26 is closed or conducting determines the average wattage input to the lamp 10. The switching means 26 preferably is a bidirectional gate-controlled thyristor, generally known in the art as a triac.

There is also provided a solid-state AC voltageresponsive switch means 30 which will conduct only when the AC voltage applied thereacross exceeds a predetermined value. This AC voltage-responsive switch me ans 30 connects between the control terminal 28 of the switch 26 and the junction 32 of the resistor 22 and the capacitor 24, in order to provide, when in a conducting state, a voltage control signal to the control terminal 28 of the switch 26 and effect a closing of same. The respective predetermined electrical values of the resistor 22 and the capacitor 24 thus provide a time constant of such value that the period of time in each half cycle of AC energizing potential at which the switch 26 is closed provides a predetermined reduced value of wattage input to the lamp 10. The voltageresponsive AC switch 30 is preferably a switch of the type which is generically known in the art as a diac. As a specific example, the diac 30 will conduct when the voltage applied thereacross exceeds about 40 volts. For this specific example, the lamp which normally operates with a power input of about 400 watts has its power input decreased to about 270 watts at nominal line voltage of 240 volts.

In an alternative lamp energizing circuit shown in FIG. 3, the lamp 10 is connected in series with a current-limiting inductor 12a, which itself forms the secondary of a loosely coupled transformer 34 the input of which is connected across the line. The add-on control device 16 is connected in series and is shown in block diagram only.

The present add-on control device 16 can also be used to dim other types of HID devices by causing them to operate at a lesser wattage and, as an example, the present add-on control device 16 can be used to dim the operation of high-pressure sodium-mercury lamps or high-pressure mercury-metal halide lamps.

In practice, HID lamps are designed to operate at one of various wattage ratings. For example, high-pressure mercury-vapor discharge lamps are designed to operate at one of various wattage ratings such as 1000 watts, 700 watts, 400 watts, 250 watts, 175 watts and 100 watts. The present add-on control device can readily be used to operate an HID lamp at a lower wattage rating, or the add-on control device can be used to operate a lamp at its rated wattage but in a ballasting circuit which would normally cause the lamp to operate at greater than its rated wattage. As a specific example, if the present add-on control device were designed to modify an existing fixture to cause a 400 watt highpressure mercury-vapor lamp to operate at about 250 watts, the resistor 22 would have a value of lOOk ohms, and the capacitor 24 would have a value of 0.047 microfarad. The switch 30 would be rated to conduct when the voltage thereacross is about 40 volts.

Operating the lamp at less than its rated wattage might be expected under some conditions to shorten the lamp life. When the 400 watt lamp reaches the end of its life, the lamp socket would be modified to alter the position of the light center of the lamp and the smaller replacement lamp would actually be rated at 250 watts which is the wattage at which the lamp would operate with the present add-on control device connected in the circuit. In this manner, existing fixtures can be revised and relamped in a simple and inexpensive manner to operate at a reduced wattage.

We claim:

1. In combination, an add-on control device connected in circuit with an HID lamp and current-limiting inductor connected in series therewith, wherein said current-limiting inductor has an inductive reactance of predetermined value to pass a current of average nominal predetermined value to operate said lamp at a predetermined wattage input when said inductor-ballasted lamp is energized by a predetermined AC potential, said add-on control device reducing by a predeter- 4 mined amount the average nominal current passed by said inductor to reduce by a predetermined amount the wattage at which said lamp will operate, said add-on control device comprising:

a. two electrical circuit paths connected in parallel and each connected to terminals which are connected in series with said series-connected lamp and said inductor;

b. one of said circuit paths comprising a series-connected resistor means and a capacitor means each having predetermined electrical values;

c. the other of said circuit paths having therein a solid-state AC control-signal-responsive switching means having a control terminal, said AC controlsignal-responsive switching means is responsive to the application of a control signal to the control terminal thereof to close during each half cycle of said AC energizing potential and to remain closed for the remainder of each such half cycle to supply electrical energy to said lamp, and the point in time during each half cycle of said AC energizing potential at which said AC control-signal-responsive switching means is closed determining the average current flow through said inductor;

d. solid-state AC voltage-responsive switch means which will conduct only when the AC voltage applied thereacross exceeds a predetermined value, said AC voltage-responsive switch means connecting between the control terminal of said AC control-signal-responsive switching means and the junction of said series-connected resistor means and said capacitor means to provide, when in a conducting state, a voltage control signal to the control terminal of said AC control-signal-responsive switching means to effect a closing of same; and the respective predetermined electrical values of said resistor means and said capacitor means providing a predetermined time constant to predetermine the time during each half cycle of said AC energizing potential said AC voltage-responsive switch means conducts to effect a closing of said AC control-signal-responsive switching means and thus reduce by a predetermined amount said average nominal current passed by said inductor.

2. The device as specified in claim 1, wherein said nominal average current passing through said inductor and said lamp will cause said lamp to operate with a predetermined wattage consumption which is one of various predetermined wattage ratings at which said HID lamps are designed to operate, and with the addition of said add-on control device, said inductor-ballasted HID lamp will operate at the next lower wattage rating for such HID lamps.

3. The device as specified in claim 2, wherein said add-on control device causes said lamp to operate at a lower wattage than the nominal wattage at which said lamp is rated.

4. The add-on device as specified in claim 3, wherein said lamp is a high-pressure mercury-vapor lamp rated for normal operation at about 400 watts, said AC control-signal-responsive switching means is a triac, said resistor means has an electrical value of about k ohms, said capacitor means has an electrical value of about 0.047 microfarad, said AC voltage-responsive switch means is a diac which conducts when the potential applied thereacross is about 40 volts, and said addon control device causes said lamp to operate at about 250 watts.

5. The device as specified in claim 2, wherein said add-on control device causes said lamp to operate at about its nominal rated wattage.

6. The add-on device as specified in claim 5, wherein said lamp is a high-pressure mercury-vapor lamp rated for normal operation at about 250 watts, said AC control-signal-responsive switching means is a triac, said resistor means has an electrical value of about 100k ohms, said capacitor means has an electrical value of about 0.047 microfarad, said AC voltage-responsive switch means is a diac which conducts when the potential applied thereacross is about 40 volts, and said adddevice causes said lamp to operate at about 270 watts. 

1. In combination, an add-on control device connected in circuit with an HID lamp and current-limiting inductor connected in series therewith, wherein said current-limiting inductor has an inductive reactance of predetermined value to pass a current of average nominal predetermined value to operate said lamp at a predetermined wattage input when said inductor-ballasted lamp is energized by a predetermined AC potential, said add-on control device reducing by a predetermined amount the average nominal current passed by said inductor to reduce by a predetermined amount the wattage at which said lamp will operate, said add-on control device comprising: a. two electrical circuit paths connected in parallel and each connected to terminals which are connected in series with said series-connected lamp and said inductor; b. one of said circuit paths comprising a series-connected resistor means and a capacitor means each having predetermined electrical values; c. the other of said circuit paths having therein a solid-state eAC control-signal-responsive switching means having a control terminal, said AC control-signal-responsive switching means is responsive to the application of a control signal to the control terminal thereof to close during each half cycle of said AC energizing potential and to remain closed for the remainder of each such half cycle to supply electrical energy to said lamp, and the point in time during each half cycle of said AC energizing potential at which said AC control-signalresponsive switching means is closed determining the average current flow through said inductor; d. solid-state AC voltage-responsive switch means which will conduct only when the AC voltage applied thereacross exceeds a predetermined value, said AC voltage-responsive switch means connecting between the control terminal of said AC controlsignal-responsive switching means and the junction of said series-connected resistor means and said capacitor means to provide, when in a conducting state, a voltage control signal to the control terminal of said AC control-signal-responsive switching means to effect a closing of same; and the respective predetermined electrical values of said resistor means and said capacitor means providing a predetermined time constant to predetermine the time during each half cycle of said AC energizing potential said AC voltage-responsive switch means conducts to effect a closing of said AC control-signalresponsive switching means and thus reduce by a predetermined amount said average nominal current passed by said inductor.
 2. The device as specified in claim 1, wherein said nominal average current passing through said inductor and said lamp will cause said lamp to operate with a predetermined wattage consumption which is one of various predetermined wattage ratings at which said HID lamps are designed to operate, and with the addition of said add-on control device, said inductor-ballasted HID lamp will operate at the next lower wattage rating for such HID lamps.
 3. The device as specified in claim 2, wherein said add-on control device causes said lamp to operate at a lower wattage than the nominal wattage at which said lamp is rated.
 4. The add-on device as specified in claim 3, wherein said lamp is a high-pressure mercury-vapor lamp rated for normal operation at about 400 watts, said AC control-signal-responsive switching means is a triac, said resistor means has an electrical value of about 100k ohms, said capacitor means has an electrical value of about 0.047 microfarad, said AC voltage-responsive switch means is a diac which conducts when the potential applied thereacross is about 40 volts, and said add-on control device causes said lamp to operate at about 250 watts.
 5. The device as specified in claim 2, wherein said add-on control device causes said lamp to operate at about its nominal rated wattage.
 6. The add-on device as specified in claim 5, wherein said lamp is a high-pressure mercury-vapor lamp rated for normal operation at about 250 watts, said AC control-signal-responsive switching means is a triac, said resistor means has an electrical value of about 100k ohms, said capacitor means has an electrical value of about 0.047 microfarad, said AC voltage-responsive switch means is a diac which conducts when the potential applied thereacross is about 40 volts, and said add-on control device causes said lamp to operate at about 250 watts.
 7. The add-on device as specified in claim 1, wherein said lamp is a high-pressure mercury-vapor lamp rated for normal operation at about 400 watts, said AC control-signal-responsive switching means is a triac, said resistor means has an electrical value of about 39,000 ohms, said capacitor means has an electrical value of about 0.22 microfarad, said AC voltage switch means is a diac which conducts when the potential applied thereacross is about 40 volts, and said add-on controL device causes said lamp to operate at about 270 watts. 